


Swear

by Rosella92



Category: Sherlock (TV)
Genre: Alternate Universe, M/M, Teenagers, Teenstrade
Language: English
Status: In-Progress
Published: 2018-06-04
Updated: 2018-10-07
Packaged: 2019-05-17 23:49:04
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 4,457
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14841545
Author URL: https://archiveofourown.org/users/Rosella92/pseuds/Rosella92
Summary: Seventeen years old Greg Lestrade just got partnered with the young and brilliant Sherlock Holmes for a class project. Sherlock has a list of rules for working with him, and the most important one is that Greg must not fall in love with Sherlock's mysterious older brother, Mycroft. Greg agrees, because he's never met the older Holmes - surely it won't be an impossible promise to keep?





	1. Chapter 1

Greg had no idea it was going to be such a crap day. Granted, it was Monday, but it started out great - Mum hadn't lectured him that morning about Kelly, and Angie was being sweet instead of her bratty preteen usual self. Will picked him up early enough that they could get cokes and bacon sarnies for breakfast, and Kelly hadn't sent any texts lecturing him about her expectations for the upcoming weekend.

It was a good day, until lunch.

Greg sat with Will and Clive, finished his sandwich early and started looking around for Kelly. It wasn't like her to be late for lunch - god knows she got on his case about it a million times - but she was nowhere to be found. Neither was Roger, Greg noticed.

Will and Clive exchanged a look. "Er...Greg...maybe they're... together," Will suggested.

Greg laughed. "Together? What do you mean?"

Clive winced. "Mate...I saw Roger give her a ride home Friday. I texted him asking what was up, but he never responded."

"Friday?" Greg frowned. Kelly had mentioned getting a ride home with a friend, but why would that be Roger? She'd never been particularly friendly with Greg's mates. Plus, now that he thought of it, she'd hardly contacted him all weekend. It had been fairly unusual - typically she insisted on him taking her out for a nice meal, or a movie. Then she'd text him about all the ways the date could be improved - a nicer restaurant, a better movie theater, a better-looking outfit for him. Once he replied he wasn't getting fitted for a tuxedo for a casual weekend date with his girlfriend, and that got him the silent treatment for almost a month.

"Christ, mate, don't make us say it." Will gave him a pained look. "There's been rumors, Greg."

"Rumors? About what, Kelly and Roger?"

"Kelly and other guys" Clive said softly. "Figured they were crap, but when I saw her with Roger...they seemed awfully close. You know."

"No, I don't know." Greg stood up, suddenly furious. "I'm going to find her, now. And she'll come back and sort all this out with both of you." He turned and stormed out, heading to the lockers near the car park. Maybe she was putting things away, like books or something...

Greg found her at her locker, lost in a kiss with Roger, one of his friends since primary school. 

He stared for a while, ready to scream, but when tears started pricking at his eyes he ran off to the toilets. He wouldn't give them the satisfaction of seeing him cry.

×××××××××××

Greg missed the next two periods, but there was an important test in his last class, Advanced Science. It was a fairly easy subject (although he was hardly the smartest kid in class), but he shared the class with both Kelly and Roger.

"Not going to let you fucks ruin my grades," Greg mumbled to himself as he entered the classroom, wiping at his eyes for the millionth time. He sat far from his usual seat in the back corner by himself, in the same row as the school's boy genius, who gave him a curious glance but kept his usual biting remarks to himself. 

Kelly and Roger sauntered in, holding hands. Roger glanced at Greg but then looked away guiltily, but Kelly merely smirked and tossed her hair as she moved closer to Roger. Greg's usual seat had been between them. He wondered how long they'd been messing around, making him look like a bloody idiot.

Greg shook his head and settled himself for the test. Luckily he'd studied, and it wasn't too difficult. He figured he got at least a B, if not an A.

After Professor Reynolds gathered up the tests, he wrote "Murder Mystery" on the chalkboard and faced the class. "I'm doing something different for your mid term projects. In lieu of a science fair, you will instead be assigned crime scenes inspired by real life murders. Your assignment is to use science to solve the crimes."

Greg perked up with the rest of the class. This would be interesting, far better than building a frothing volcano or growing plants with artificial light. 

"You will also be working with an assigned partner."

The room filled with groans.

"Enough of that! I will be announcing the teams now. You'll sit with your partner and come up with a team name. Tomorrow I will pass out your assignment and go over the rules." Professor Reynolds cleared his throat. "Yvette Saunders, you're with Abby Fields. Kelly Bowler, you're paired with Marie Weinmen. Greg Lestrade, you will be working with Sherlock Holmes."

The young boy gave Greg another glance, then frowned and looked back at his notebook and wrote furiously in it. 

_Okay..._ Greg put on his friendliest grin and made his way over to the boy. Sherlock Holmes was not very popular, mostly because he had a tendency to keep to himself when he wasn't blurting out cruel observations about everyone else. His acerbic nature hadn't reached Greg - at least, not yet - so partnering with Sherlock didn't bother Greg at all. He was obviously brilliant, since he skipped a number of grades and was the only thirteen year old in Greg's class. The boy was probably scared, so he lashed out. Besides, he was older and undoubtedly more mature than Angie, and Greg had to live with her.

This would be fine.

Greg sat in the empty chair next to Sherlock. "Hey, so I guess we're going to be partners - "

"No."

Greg frowned. "Wait, what?"

"No. I work alone, and will continue to so."

The room was filled with people chatting away, some laughing as they came up with team names. Greg was the only one staring at his partner in shock.

"You...hey, we have to work together..."

The bell sounded. Sherlock quickly picked up his things and left. Greg gaped after him, then followed.

"Hey! C'mon!"

He darted through rows of students hurrying to buses and cars, following the young boy as he made a beeline to the car park.

"Sherlock! Please!" The idea of having to do the project alone, or not getting credit for it, was the final straw to this horrible day. "I have to work with you! I _want_ to work with you!"

That made Sherlock stop. Greg nearly crashed into him. 

"Gregory Lestrade." Sherlock turned and stared at him intensely. "I will work with you, on a few conditions."

Greg exhaled. "Fine. What are they?"

"You will not allow yourself to become distracted and therefore useless as a partner on this project."

"Fair enough. What else?"

"You will follow my instructions without fail and supply me with anything I demand."

"You sound like my ex-girlfriend." Greg laughed bitterly. "Well, if it's to do with the project, and it's nothing too crazy, sure. That all?"

"No." Sherlock stepped forward, his expression deadly serious. "The final one is most significant."

Greg nodded. "What is it?"

Sherlock took another step forward, invading Greg's space. "You must swear that you will not fall in love with my older brother."


	2. Chapter 2

"Wait, wait..." Sally was trying not to laugh hysterically and utterly failing at it. "He made you promise what exactly?"

It was only a few minutes into his tutoring session, but Sally was one of his close friends and wanted all the details from what happened with Sherlock. She didn't like the boy - she even referred to him as a "freak" until Greg made it clear that he didn't like that - but was intrigued by the ultimatum given by the young genius.

"You heard me!" Greg said, grinning himself. "Can't fall for his brother, or I don't get credit for the project."

"So? You're not going to fail. You're my bloody science tutor, after all."

Greg snorted. "That's not the point. This project is a huge part of our grade."

Sally shrugged. "Again, so?"

"I'm not getting a crap grade because of Sherlock Holmes!"

"Oh, please. Anything less than an A doesn't mean it's crap."

Greg scoffed. "It is if I get it because Sherlock won't give me credit for my work on the project!"

"Wait a second." Her nose crinkled. "Greg, are you planning on falling for Mycroft Holmes?"

"What? No! I haven't even met the man."

Sally smirked. "At least now we know he exists."

Greg smiled at the thought. Sherlock had barely mentioned his brother in the past, but the rumors were intriguing. There was talk that he was a spy, or an assassin, and was powerful enough to make people disappear. He was rumored to be interning for the government, or even the royal family. Or both.

There were also rumors about his appearance. Once, Sherlock was picked up in a limo after school, and Erica McConner was close enough to hear him address the man sitting in the limo as his brother. She quickly positioned herself to get a better look at the mysterious elder Holmes brother. According to her, Mycroft Holmes was tall and thin, with dark wavy hair and a sharp profile, and wore a perfectly tailored expensive suit. He was, she declared, the sexiest man she had ever seen in her life.

And now Greg was going to be even closer to the elusive elder Holmes brother, but was actually forbidden to fall in love with him.

Did that mean that Sherlock meant for them to meet? If they studied at Sherlock's home - an actual mansion, if the rumors were true - was Greg inevitably going to run into the mysterious, quite possibly dead sexy Mycroft Holmes?

"Hello? Greg!" Sally was waving her hand in his face, bringing him back to reality. "God, you're already in love with him!"

"No, I'm not! I'm just...thinking."

"You're practically drooling." She sighed and opened her textbook. "Okay, Romeo...time for science. If I don't ace my next test, my parents will have my head."

"Yes, your majesty." Greg settled next to her and was about to start on their next assigned chapter when his phone buzzed. He was going to ignore it, figuring it was Angie being a typical bratty little sister, but then it buzzed again. And again.

"Whoa." Sally raised an eyebrow. "Tell me that's not Kelly."

"Better not be." Greg frowned at the unrecognizable number, but then read the messages and knew exactly who they were from. 

**_\- I have sent you the coordinates of my home. We will meet there tonight. Arrive at seven._ **

**_\- And no, I will not visit your home. I have no wish to meet your family._ **

**_\- Remember your agreement._ **

**__**

×××××××××××

Sherlock's home was a _palace._

There had to be almost 100 acres of lush forest and gardens surrounding the estate, which was like a smaller version of Versailles. Inside were gorgeous pre-Raphaelite paintings on the walls, sculptures in corners of every room, ornate rugs over marble floors...it was like a bloody museum.

"Don't touch anything," Sherlock snapped, and led him up a winding staircase. Once they got up to the landing the younger boy whirled on him and pointed to a closed door.

"That is Mycroft's room. It is, of course, off limits. You must honor your agreement!"

"Fine, fine!" Greg held his hands up. "Is he even here?"

Sherlock sneered. "My brother is not to be disturbed."

_Oh. Oh wait. Holy shit._ "So he is here today?"

"You shan't visit him!"

"Yes, I know! But...what if he comes out of his room?" _I have to at least see him...see if he's as beautiful as Erica said he is..._

"If my brother leaves his room, you will make yourself scarce. Now follow me." Sherlock turned and led Greg to another closed door, which he opened carefully and strode inside.

Greg looked inside and nearly gasped. He'd expected a huge, beautiful room, but while it was gigantic (almost the size of his whole house), it was a disaster. Papers were strewn all over the floor. The walls were covered with graffiti and scribbled notes. Vials of varying shades of liquid sat on Sherlock's desk, which had a knife stabbed in the middle of it. 

Then there was the skull on the mantle.

"Christ!"

Sherlock waved his hand. "Oh, it's no one you know. A generous man left his body to science. Father gifted the skull to me last year. A birthday present."

"Erm." Greg cleared his throat. "I got a hamper for my birthday. Chocolates. Sweets. Movie tickets."

"Dull." Sherlock loftily perched himself on his desk chair and steepled his fingers together. "Now. Whose murder shall we envision?"

Greg was halfway through sitting on Sherlock's bed and ended up collapsing on it. "What?" 

"Our project." Sherlock huffed. "Surely you have not already forgotten?"

"We're supposed to solve a murder, not commit one," Greg said, settling himself on the bed. It was unmade, but otherwise clean. 

"One must think as a criminal to catch him."

"So, you want to do some profiling."

The younger boy looked pleased. "Yes."

"Okay, great, but I'm not even pretending to plan the murder if someone we know."

"Very well. Now. What would drive a man to do this to his victims?" He plucked a sheet of paper from his desk and handed it to Greg.

Greg frowned at the diagram. "Jesus. This look like...oh shit. Professor Reynolds gave us a case based on Jack the Ripper."

"Problem?"

"It's probably the hardest case he assigned." Greg looked up and flashed the boy a grin. "This'll be fun."

Sherlock stared at Greg in unabashed shock, then actually smiled. "Quite."

They'd already mapped out potential murder weapons and suspects when Greg called for a lunch break.

Sherlock glared in disgust as Greg unwrapped a granola bar. "Yes, good thing criminals also adhere to a stringent lunch schedule. How kind of them to allow you to divulge in a snack."

"Everyone has to eat, genius." Greg offered a spare bar to Sherlock, who waved it away. "Have it your way."

"Gluttony. It is a loathsome feature you share with my brother."

Greg gulped. "What? Mycroft isn't fat."

Sherlock's eyes grew wide. "And how do you know that?"

"Erica McConner saw him once. She said he's tall and thin."

"If she failed to notice his extended stomach, then she is a remarkably unreliable source." 

"Mmhmm." Greg finished his granola bar and gave the younger boy a curious look. "How did you know I like other men?"

"The way you ogle the male students is absurdly obvious."

Greg snorted. "Sure. So why not Mycroft?"

"I have my reasons!"

Greg winked. "Want me all to yourself, do you?" 

Sherlock sputtered. "You are abhorrent! I would sooner mate with a petri dish overrun with spores!"

"Gee, thanks." 

"Do not tell me that you find me attractive. I will vomit."

"For God's sake. You're only thirteen."

"You are only four years older than me."

"There's a big difference between thirteen and seventeen, mate." Greg stood up and looked around. "Where's your washroom?"

Sherlock pointed at the door. "Down the hall, to your left. Be swift."

×××××××××××

Greg washed his hands and peeked out into the hallway.

Mycroft's room was _right there_. And...the door was open.

Just a peek. Why not? 

It was a stupid arrangement anyway, Greg reasoned as he approached the room. There was nothing wrong with being curious about Mycroft Holmes. Maybe the mysterious Holmes brother would even be...

"No, certainly not. I can assure you, such precautions will not be necessary."

_That voice._ Soft, sensual. Posh. Greg stopped in his tracks. 

"The ambassador shall hear from me no later than six o'clock."

Slow. If he walked slowly, he could look inside. Just see the man. One look.

"I trust all accommodations have been prepared."

A few more steps. No creaking boards yet. Slow, careful...

A man stood in the middle of the room, his back to the slightly ajar door. He had a dark blue suit that fit perfectly against his slender frame. One hand in his pocket, the other cradling a mobile phone. Long fingers. A ring. _Fuck! Married? Is that why Sherlock..._

All thought escaped Greg's mind when Mycroft Holmes turned.

_Beautiful. Oh God..._

Soft red curls. Strong, sharp features. Those lips...oh shit, his tongue...to lick his upper lip...

Greg wanted to be able to move, to say something. Anything. But all he could do was stand motionless, eyes wide, as Mycroft turned again, staring right at Greg.

There was a brief moment when Greg was able to see the shade of Mycroft's eyes. Light blue, gray. The color of stone.

Then, the man spoke.

"One moment." The phone was curled away from him as he raised an eyebrow at Greg. "And who are you, exactly?"


	3. Chapter 3

"I..." Greg stared, his pulse racing. "I'm..."

Mycroft only stared back. "You're...?"

"Err..." _Oh God. He's so beautiful. Those hands, those lips..._ "You, um...you're. I'm..."

Gray eyes narrowed at him. "Yes?"

"I'm...I'm Greg." A door behind him creaked, and he panicked. "Shit! Don't tell Sherlock!"

With that, he turned and ran back to the younger Holmes's room. His heart was nearly beating out of his chest.

_I saw him. I saw him. He's beautiful..._

_Oh god, he saw me too._

Luckily Sherlock was distracted when Greg hurried in, nearly breathless. The younger Holmes brother was sprawled out on the floor, surrounded by sketches of dismembered corpses. Sherlock's right arm was covering his eyes, and his left clutched a pen. "Did you get lost?" he drawled.

"Eh. Yes. A little." Greg sat on the bed. "Doing some drawing?"

"Brilliant deduction. Clearly a career in criminal investigation awaits you."

Greg was about to reply when a smooth posh voice called out. "Brother. Please clarify something for me."

Panic shot through Greg's body. He froze, while Sherlock scrambled to his feet, kicking at the drawings. "Hide!" he hissed. 

"What? Hide? Are you serious?"

"In there!" Sherlock pointed to his closet. "Now! Before he comes in!"

"Christ!" Greg hurried into it and shut himself in, squeezing in between posh clothes. The poetic irony of hiding in the closet wasn't lost on him. 

Greg tried to breathe quietly as he watched Sherlock through the slitted doors of the closet. The boy cast a wild look in his direction, then stomped to the door, papers flitting wildly in the air as he hurried to open it.

In the doorway stood Mycroft Holmes. Tall, gorgeous...and clearly annoyed.

"Dear brother," he intoned. "Do you have a guest that you neglected to tell me about?"

"No," Sherlock answered curtly, and tried to close the door. Mycroft stopped it with his foot. 

"Are you quite certain, little brother?"

Sherlock paused. "You haven't...seen anyone, have you?"

Greg's heart was beating so loudly, he was sure it could be heard across the room. He tried to slow his breathing, wanting to calm himself down.

Mycroft smirked. "I have not, brother mine. Yet I was quite certain I heard you speaking to someone."

Greg's jaw dropped. Mycroft Holmes just lied to cover for him. Did this mean...?

Sherlock snorted. "Well, dear brother, perhaps your senses have been obfuscated by hunger. I imagine it's been a full ten minutes since you've eaten. You must be famished." 

Mycroft rolled his eyes. "Very well. Carry on with your..." His eyes searched the room and landed on the closet. His gaze seemed to lock with Greg's.

"... Experiments." Mycroft put a disdainful emphasis on the word, scowled at Sherlock, then left.

Greg waited until Sherlock closed the door, then slowly opened the closet. "Christ. That was close."

Sherlock whirled on him. "Keep your voice down!" he growled. "He might hear you!"

Greg rolled his eyes. "What is the big deal?" he whispered. "This is weird, sneaking around!"

"We have an agreement!"

"It's a fucking weird agreement! I can't meet your brother? So what if I do? So what if I like him, or he likes me!"

Something flickered in Sherlock's eyes. Greg couldn't tell if it was fear or anxiety.  
"He did not see you, did he? Tell me he didn't!"

"I want to know why it matters!"

"I've explained! You are not meant to...be together!"

Greg scoffed, then paused. "Oh."

"Oh?"

"I get it," Greg said softly. 

Sherlock stomped to his desk, sorting through papers. "I sincerely doubt you grasp the concept of..."

"No. No, I understand why you don't want me to meet your brother." Greg felt his throat tighten and turned away, picking up his bag. "It's that I'm not good enough for him, isn't it?"

Sherlock stared at him. "You're..."

"Yeah." Greg tried to laugh, but it just sounded hollow. "I get it, all right? He's brilliant... gorgeous... important. And I'm some common idiot. I get it. You didn't want to work with me, you obviously still don't... forget it. I'm an idiot. Bloody fucking idiot."

He turned to the door, gently opening it, and walked through it.

Sherlock did not stop him. He didn't say a word.

×××××××××××

Greg left the Holmes mansion without seeing anyone else. He headed past the estate grounds, figuring he'd call a ride once he was far enough away.

What was wrong with him? Kelly didn't want him. Roger didn't want him as a friend. Sherlock didn't want him as a working partner, or a friend. And he certainly didn't want him dating his brother. 

Maybe he was more of a fucking loser than he felt he was when he saw Kelly kissing Roger. Maybe Sherlock was right. Maybe...

A car came up behind him, slow and creeping. Greg stopped, his pulse jumping. Was it a Holmes servant, making sure he left?

The car pulled up further, then stopped. The backseat window rolled down, and Mycroft Holmes gazed out at him.

"Gregory Lestrade?"

Greg gaped in shock, then nodded.

Mycroft smirked. "Get in."


	4. Chapter 4

_He wants me to get in the car._ The suggestion of it was damn near overwhelming. The reality of the situation set in - a stranger, luring him like a bloody siren. Greg frowned and shook his head. "I'm not sure that would be a good idea."

"For heaven's sake." Mycroft rolled his eyes. "I do not have nefarious intensions. My driver will take you home. I merely want to discuss an...arrangement."

"...A-Arrangement?"

Mycroft smiled, and Greg's world changed. "Indeed."

×××××××××××

_Not going to stare...not going to stare...oh god...those hands..._

The car rocked gently as Mycroft Holmes sat across from Greg and merely stared at him. Greg tried not to fidget, but he knew he was being scrutinized.

After everything, all of Sherlock's warnings, Mycroft was here, and they were alone. 

The man was incredibly handsome. Greg knew he was staring back, but couldn't help it. Those eyes, that nose, that hair...and those hands, with long slender fingers that could tease and caress...

"You have not known my brother long." Mycroft smiled, looking nearly villainous. "That is, not personally. You knew of him, but never approached him. And now, you are working with him on a project." 

"Ah...yeah."

Mycroft chuckled. "He told you to keep your distance from me."

"...Yeah."

"And yet here you are."

Greg swallowed. "Here I am." _With you._

"Very interesting." Mycroft folded his hands. "What do you know of the nature of my employment?"

"I know you're important."

Mycroft raised an eyebrow. "You're very succinct."

Greg fought the urge to squirm. "What sort of arrangement were you talking about?"

A wicked smile from Mycroft made Greg's pulse race. Then he spoke, and Greg could only listen in a daze.

×××××××××××

As soon as he got home, he texted his friends as instructed.

**\- I met someone amazing...I think I've found the one. I'm serious.**

_"You will tell your friends we have started seeing each other. You will tell them to keep it a secret. If you feel they cannot keep a secret, do not tell them. Sherlock must not be made aware."_

Mycroft had stated that Greg would be rewarded. He didn't want money, but Mycroft offered "something far more substantial". An internship at the police department, and to be set on a path for the junior detective program.

_"What's in it for you?"_

_This had made Mycroft laugh. "I wish to see if Sherlock will be able to deduce it. He can be absent minded when it comes to sociological normalities. I also wish to see how well you can act under pressure. If our first meeting is any indication, you will not be suitable for detective work."_

_Greg had met his gaze, willing his heart rate to calm. "I can do it."_

_"We shall see, Gregory."_

×××××××××××

That night Greg lay in bed, staring at the ceiling.

He had a boyfriend now. Mycroft Holmes. Well, it was a fake relationship, but whatever it was, it was with him.

The gorgeous, sexy, brilliant, fascinating Mycroft Holmes. 

_"You do not turn eighteen until next month. Do not suggest anything besides flirtation until approximately four months from now."_

_"Four months?"_

_"Of course. It would be immoral otherwise._

_"Right, yeah, but what would we...?"_

_"Leave it to me, Gregory."_

A text jolted him out of his thoughts. Greg rolled over and grabbed his phone.

**Your conclusions are incorrect. -SH**

Greg sat up, frowning. He scrolled through his phone and called the number.

"Lestrade." Sherlock spoke in his usual clipped manner. "Your deduction methods are lacking in the basest of skills. As your partner on our project, I am concerned."

"Yeah, hi to you too. What am I wrong about, then?"

Sherlock was quiet for a moment. "Mycroft is unsuitable for relationships. You clearly desire emotional and physical intimacy. He can provide neither."

Greg shook his head. "You're trying to protect me?"

"Don't be absurd," Sherlock snapped. "I merely want to prevent a catastrophe."

"Right." Greg smiled to himself. "I'll talk to you tomorrow, then."

Sherlock was quiet again. "Lestrade. Are we...?"

"We're fine." Greg grinned. "Get some sleep."

After he hung up, Greg saw he had a text from Sally. 

**OMG is it Mycroft you met Mycroft TELL ME EVERYTHING**

Greg chuckled and sent a reply that they'd talk tomorrow with a wink emoji. 

Clive sent a text as well. **Met someone huh? M or F or other?**

_M - tall, gorgeous, smart as fuck_ was Greg's reply. 

This was weird. A fake relationship, kept secret from his fake boyfriend's brother, and in exchange getting a head start in his dream career.

Fucking weird, is what it was.

But nothing harmful would come of it. Sherlock would be kept in the dark about the whole arrangement, and Greg would get to have access to an exclusive internship. 

Simple, really. Pretend to be in a relationship, don't tell Sherlock. 

Nothing could possibly go wrong.


End file.
